The present invention generally relates to friction stir welding and, more particularly, to the use of friction stir welding for the weldbonding process.
Friction stir welding is commonly used in joining two or more work pieces for various classes of materials, such as aluminum, magnesium, copper, titanium and steel. This method of welding in lap, L-joint and T-joint configurations leads to a small weld nugget size with notches on both sides of the weld nugget. Due to a higher stress concentration on either side of the weld nugget, these notches increase stress concentration factors, and reduce fatigue life.
Moreover, friction stir welding of two or more work-pieces does not seal gaps between these work-pieces as in adhesive bonding. The use of adhesive bonding is increasing dramatically as it eliminates drilling holes and installation of fasteners. It is highly desirable to replace fasteners, fusion, friction, and spot welded joints with adhesive bonded joints. Adhesive bonded joints spread loads more evenly and result in smooth surface conditions. In particular, adhesive bonding results in the elimination of stress risers at fasteners and weld locations. The automotive industry has used adhesive bonding of auto parts to increase surface finish, increase structural damping, and eliminate failure of spot welds which results in vibration noise. However, adhesive bonding of complex curvature structures is quite expensive because specialized bonding tools are required to apply pressure during curing of the adhesive. Furthermore, at room temperature, the curing of adhesive can take several days.
Weldbonding is a hybrid method of assembly that utilizes both the welding and adhesive bonding processes. Edison Welding Institute (EWI), Columbus, Ohio, developed a process using adhesive bonding accompanied or followed by laser welding. Laser weldbonding has been used on small airframe structures such as small commuter aircraft fuselages. However, laser weldbonding requires expensive equipment and the quality of the laser welds is poor. For example, laser weldbonding is difficult to use on aluminum structures, and the success of the laser weldbond depends greatly on the aluminum alloy the structure is comprised of. The auto industry has used adhesive bonding with fusion spot welding of steel. However, fusion welding of aluminum, which is used in new generation cars, is quite difficult and costly. In addition, fusion spot welding uses electrodes which creates surface indentation on both upper and lower surfaces, resulting in poor surface conditions. The fusion weld also causes adhesive to splatter, thus reducing bond quality.
As can be seen, an inexpensive and effective weldbonding process is needed that will maintain two or more work-pieces together and apply pressure during curing of an adhesive without the use of any bonding tools, and will result in smooth surface conditions and evenly sealed joints for a variety of materials.